Controlling the interior noise level within an aircraft is a major concern for aircraft manufacturers and operators. One major source of noise is the turbulent boundary layer (“TBL”) noise on the aircraft's exterior surface. Referring to FIG. 1, TBL wall pressure fluctuations 125 typically take the path of least resistance to transmit noise into the interior cabin 150 of an aircraft. One of these paths is through the buildup formed by the fuselage's skin 105, a sound absorptive layer 107, and interior closeout panels 110. This path is referred to as the “acoustic path” 140, which generally has high transmission loss. Another path is the “structural path” 150 formed by interior structures that are mounted to the fuselage airframes. These interior structures are often mounted to the fuselage with vibration isolators. However, these vibration isolators form a potentially ‘easier’ path for the TBL noise to transmit to the interior cabin at high frequencies.
Referring to FIG. 2, conventional aircraft vibration isolation systems 200 typically include a single vibration isolator 215 disposed between an aircraft's fuselage 205 and a cabin interior closeout panel 210. The aircraft may have a multitude of these single isolator systems 200 disposed throughout the space between the fuselage 205 and cabin interior closeout panels 210. However, conventional single isolator systems 200 still allow significant noise into the interior cabin of aircraft. Single isolator systems also may transmit more noise to the interior cabin for a composite fuselage compared to an aluminum or other metallic fuselage.
One method of vibration isolation for aircraft involves using heavier closeout structures. This additional weight can impair the performance of the aircraft.
Accordingly, a need exists in the art for an improved vibration isolation system for reducing noise in interior aircraft cabins without adding unnecessary weight to the aircraft.